Bi-tangential Scleral CLs – Drawing a Straight Line to Clinical SuccessCapricornia Contact Lens has been producing custom made contact lenses in Brisbane for 35 years. During this time, the laboratory has developed some innovative rigid contact lenses, including novel scleral contact lenses incorporating a bi-tangential peripheral curve design. In this CPD article, optometrist David Stephensen reports on a study that analysed the effectiveness of a bi-tangential peripheral curve scleral contact lens designed by Carpricornia Contact Lens. WRITER David Stephensen LEARNING OBJECTIVES On completion of this CPD activity, participants should be able to: 1. Understand the design principals of the bi-tangential peripheral curve scleral contact lens, 2. Realise the various indications for use of this lens, 3. Be aware of a study designed to analyse the effectiveness of the lens, and 4. Understand the improvements in visual acuity that scleral lenses achieve, compared to spectacle correction or uncorrected visual state Scleral contact lenses are an important tool in medical contact lens practice for visual rehabilitation of patients with corneal pathology, such as irregular anterior corneal astigmatism or corneal opacity. Scleral contact lenses may be defined as a contact lens manufactured from a rigid gas permeable polymer that has its landing zone on, or beyond, the corneal limbus. This portion of the ocular surface often has a greater degree of morphological regularity than the pathologically affected cornea. Scleral contact lenses may provide a viable solution for patients with corneal irregularity whose vision cannot be improved with rigid corneal contact lenses. The irregular nature of the cornea may induce poor lens centration or an inability to maintain an appropriate fitting relationship with the anterior corneal surface. By transferring the fitting relationship to the more regular limbus and vaulting the irregular cornea, patients can achieve an improvement in fit, vision and comfort. Some cases of nonhealing corneal epithelial defects and other ocular surface diseases do not resolve with currently available therapeutic modalities, which include eye patching, topical ocular lubrication, soft bandage contact lens wear, tarsorrhaphy, and the surgical application of amniotic membrane. In these cases, scleral contact lenses may have a therapeutic application by providing a barrier and reservoir to improve the local ocular surface environment, promoting healing. Several investigators reported on the use of scleral contact lenses for a variety of indications, including ocular surface disease,1keratoconus, 2moderate-to-severe dry eyes, and penetrating keratoplasty or deep anterior lamellar keratoplasty. 3,4,5Van der Worp et al 6characterised the scleral profile and found that the anterior scleral area is generally more toric than the limbal area. Their analysis also revealed that for most eyes, the anterior sclera may be modelled using a tangential profile, rather than a curve. 6,7Hall et al 8assessed the superior, inferior, nasal, and temporal scleral junction angles and found that 77% of all transition angles demonstrated an almost tangential extension of the cornea to form the peri-limbal sclera in these cases. This mathematical description of limbal geometry is the principle that lends itself to the utility of a bi-tangential peripheral curve scleral contact lens design, as produced by Capricornia Contact Lens. To achieve these outcomes, a contact lens design that provides a reliable and durable outcome is essential. The bi-tangential design of Capricornia Contact Lens’ scleral contact lens allows the practitioner to deftly modify the edge parameters of the scleral contact lens to achieve a functional fitting outcome for patients. To explore the scope of the success of these bi-tangential scleral contact lens designs, Capricornia Contact Lens initiated a study to measure the real-world outcomes at practitioner level. METHODOLOGY The bi-tangential scleral contact lenses studied were designed and manufactured by Capricornia Contact Lens, Brisbane, Australia. The contact lens consists of a spherical back optic zone of 10mm, and a midperipheral zone to vault the limbal zone of the cornea. The contact lenses were manufactured in hexafocon B material (Boston XO, Bausch & Lomb) ((Dk 141 × 10-11 cm3 O2(cm)/ [(sec.) (cm2) (mmHg)), with nominal central thickness values of 300μm, 420μm and 600μm. The transition at the midperipheral zone is blended to be smooth and connects the optical zone with the peripheral landing zone of the contact lens. The contact lens design uses nonspherical blended zones to create a smooth, tangential connection between the back optic zone radius, the limbal clearance zone, and the landing zone. Additionally, the transition zone and landing zone for the Epicon lens are each designed as a frustrum of a cone. This is defined as a straight line that can be constrained by a cone angle and a zone width; the width being defined by the outermost diameter of the reverse curve zone and the outermost diameter of the lens. This retrospective study included 526 patients (718 eyes) whose management included the use of a scleral contact lens (Epicon and KATT, Capricornia Contact Lens, Brisbane, Australia). The data was obtained during regular in-practice clinical visits conducted from January 2022 through to April 2022, from 91 ophthalmic fitting centres and clinics in Australia, New Zealand, and Singapore. One data set per patient was used in the analysis. The scleral contact lens is indicated for daily wear. Patients’ intended purpose for scleral contact lens wear includes visual correction for myopia, hyperopia, astigmatism, presbyopia, and/or treatment of keratoconus, ocular surface disease, irregular cornea, post-corneal surgery or dry eye. Patients were excluded from this study if they had any systemic disease that might affect the eye, or be exaggerated by wearing the contact lens; if an allergic reaction of the ocular surface or adnexa might be induced or exaggerated by wearing the contact lens; if they had an allergy to care solutions or any ingredient in a solution to be used to care for the scleral contact lens; any active corneal infection (bacterial, fungal, or viral); or whose eyes became red or irritated. The primary outcome was the visual acuity improvement of the patients at the time of the most recent clinical aftercare consultation. Uncorrected visual acuity (UCVA), best corrected spectacle visual acuity (BSCVA) and visual acuity with scleral lens (BCLVA) were examined. In this study, adverse reactions and other safety conditions were also reviewed during the overall wearing period. No adverse reactions were reported at the end of the follow-up period. “ Scleral contact lenses may provide a viable solution for patients with corneal irregularity whose vision cannot be improved with rigid corneal contact lenses To obtain consistent vision results across the practices, scleral contact lenses were rinsed well with fresh, sterile rinsing solution, prior to insertion. Each scleral contact lens was placed on the eye with several drops of non-preserved saline inserted into the bowl of the contact lens. Patients in this study were typically wearing their scleral contact lenses for 12–16 hours a day, with the maximum wearing time not exceeding 16 hours per day. RESULTS DemographicsThe demography of the clinical population is shown in Table 1. The results are broken down by patient ethnicity to facilitate analysis of the efficacy of limbal fitting across different ethnic groups. Ethnicities are described as a modified version of the Australian Bureau of Statistics Australian Standard Classification of Cultural and Ethnic Groups (ASCCEG) 9: North-Western European (NW European) for patients of Caucasian descent; Southern and Central Asian (SC Asian); North East and South East Asian are combined as Asian; North African and Middle Eastern are combined as Middle Eastern; Sub-Saharan Africa are referred to as African; and Oceanian covers the Pacific Ocean peoples. The numbers reported are for eyes reporting data. Time Worn The average time worn for the eyes studied was 21.65±7.38 months. The shortest wearing time was four months and the longest was 48 months. Figure 1 shows the frequency distribution of wearing time. Visual Acuity Visual acuity measurements are reported in decimal notation for the purposes of mathematical modelling. In decimal notation, the Snellen fraction is converted into the decimal equivalent, where 6/6 would represent 1.00 and 6/60 would represent 0.01. Testing the UCVA, BSCVA and BCLVA samples for normality using the Jarque-Bera test showed all three samples to be normally distributed. Single factor ANOVA (Excel, Microsoft, Redmond) showed that the UCVA, BSCVA and BCLVA samples were not equivalent. Post hoc t-test showed that the means of all samples were different to a statistical significance level of p<0.05. Figure 2 shows the box and whiskers plot of three data sets that visually demonstrate the improvement in visual outcomes created by the fitting of scleral contact lenses to this patient population. To explore whether the visual acuity benefit occurred in both populations with irregular corneas and those with dry eyes, a Mann- Whitney U test was used to compare the BSCVA and BCLVA for the dry eye cohort. No significant difference was found between BSCVA and BCLVA in the dry eye cohort (p=0.1), indicating that the scleral contact lenses correct the underlying ametropia in the same fashion as spectacles for a dry eye cohort. Relationship Between Back Vertex Power and BCLVA The back vertex power of the individual contact lenses was converted into Fourier Power Vector notation of M, J0, J45, where M is the spherical equivalent of the contact lens and J0 and J45 describe the astigmatic correction inherent in the contact lens back vertex power. The M value was then adjusted to create an equivalent back vertex power at a nominal back optic zone radius (BOZR) of 7.9mm to create an equivalence across the data set. The adjusted absolute M value showed a poor, negative correlation with BCLVA of R2 = -0.119. Incorporating the J0 and J45 into a quantification of the magnitude of the power vector did not improve this correlation, resulting in R2 = -0.117. Equivalence of BCLVA Across Ethnicity-based GroupsTo demonstrate the effectiveness of the scleral contact lenses across the different ethnicities, the BCLVA was compared for each ethnicitybased sample. Due to the small size of the South Central Asian, Middle Eastern, and African ethnic groups, it was not practical to test for normality and a Kruskal-Wallis non-parametric test was used to compare the different demographic groups. The Kruskal-Wallis test showed there were differences between the different ethnic populations (p=0.02). Excluding the two smallest samples – the South Central Asian and African – the remaining ethnic groups of North-Western European, Asian, Middle Eastern and Oceanian were shown to have equivalent BCLVA performance with the scleral contact lenses (p=0.09). DISCUSSIONImprovements in visual outcomes are a primary motivation for the use of any optical appliance in eye care. The main indication for scleral lenses is optical correction of an irregular corneal surface, commonly due to keratoconus or corneal transplantation. Schornack et al 10found an improvement of 2.9 lines and a median Snellen visual acuity of 6/6 when fitting scleral lenses in patients with keratoconus. Kreps et al 11demonstrated excellent clinical outcomes of scleral contact lens fitting in patients with keratoconus, with significant improvement of both VA and vision related quality of life. Scleral contact lenses were reported to provide good high- and low-contrast visual acuity and high patient satisfaction in patients with keratoconus. 12Shorter et al reported on a significant proportion of eye care providers – 34% of respondents – for whom scleral lenses were the first option for management of corneal irregularity.13In this study, coordinated by Capricornia Contact Lens to examine the benefits of bitangential scleral contact lenses, the overall cohort mean BSCVA achieved by the bitangential scleral contact lens patients, was a statistically significant improvement in visual acuity of 0.21. Scleral contact lenses offer patients with anterior corneal surface irregularity the opportunity to improve their visual acuity. When the sub-population with dry eye is excluded from the visual acuity analysis, the improvement in visual acuity from BSCVA to BCLVA increases to 0.24. In Snellen visual acuity terms, this represents an increase in visual acuity from 6/10 to 6/7,3making the visual acuity improvement not only statistically significant but also clinically significant. This improvement in visual acuity, that may be achieved using the bi-tangential scleral contact lenses from Capricornia Contact Lens, demonstrates that these contact lenses have a valuable place in clinical contact lens practice.“ Patients’ intended purpose for scleral contact lens wear includes visual correction for myopia, hyperopia, astigmatism, presbyopia, and/or treatment of keratoconus, ocular surface disease, irregular cornea, post-corneal surgery or dry eye The improvement in visual acuity of two Snellen chart lines is consistent with other reported outcomes. Suarez et al14noted a similar two-line improvement from BSCVA to BCLVA but in a much smaller cohort. This new study shows that this improvement in visual acuity occurs across much larger samples and suggests that the visual acuity benefits of the bi-tangential scleral contact lens design methodology are applicable to the population of patients with anterior surface corneal irregularities.The finding, that the visual acuity improvements were independent of back vertex power and spherocylindrical correction, is also of note. This indicates that the underlying axial ametropia of eyes with corneal irregularities will not negatively affect visual acuity improvements that have been demonstrated with the bi-tangential scleral contact lens design. In simple terms, the use of the bi-tangential scleral contact lens itself is the factor that improves visual acuity, irrespective of the magnitude of the back vertex power. The bi-tangential scleral contact lens design is, therefore, applicable to patients with underlying axial myopia, emmetropia or hypermetropia. An additional indication for the fitting of scleral contact lenses is for the management of dry eye. The TFOS DEWS II Management and Therapy Report15includes reference to the benefit of scleral contact lenses in maintaining a tear reservoir and assisting in the preservation of the ocular surface. The sample cohort in this study included a population of patients who wore bitangential scleral contact lenses for management of dry eye. On average, these patients had worn scleral contact lenses for 20.68 months, demonstrating a persistence of use. No gain in visual function with respect to BCLVA or BSCVA was noted in these patients. With the persistence of use demonstrated in the absence of a visual acuity improvement, it is reasonable to assume that this sub-population of dry eye patients wearing the bi-tangential scleral contact lenses is achieving a clinical benefit in the management of their dry eye.“ This study provides confirmation that the fitting of scleral contact lenses, specifically those with bi-tangential peripheral design, creates beneficial visual outcomes for patients In an increasingly multicultural world, potential anatomical variations that may arise due to ethnicity, should be accounted for in scleral contact lens fitting. Consejo et al reported that statistically significant differences in scleral sagittal height may be encountered between Caucasian and Asian patients. These sagittal height differences require a peripheral curve design that is adaptable across a range of scleral shapes, irrespective of ethnicity. To explore whether the bi-tangential scleral contact lens will function irrespective of ethnicity, the visual outcomes were compared across ethnicities. Two of the identified ethnicities, African and South Central Asian, were underrepresented in terms of sample size, and were excluded from the comparison. The remaining ethnicities of North-Western European, Asian, Middle Eastern and Oceanian demonstrated equivalent BCLVA performance with the bi-tangential scleral contact lens design. This suggests that the bi-tangential scleral contact lens design may be considered for patients solely based on the underlying clinical indication, and that different scleral contact lens designs are not required for different ethnic groups if a bi-tangential scleral contact lens design is available to the contact lens practitioner. Adverse reactions were investigated during the study period. No adverse reactions, including infectious keratitis or other severe complications related to scleral contact lens wear were observed in any of the patients. This indicates the safety of the bi-tangential scleral contact lens design in an established wearer cohort. Patients were advised to wear their scleral contact lenses for an average of 12 hours per day to improve long-term tolerance of the scleral contact lenses, and to balance theoretical corneal hypoxia-related complications. No evidence was found that would provide contraindications for fitting bi-tangential scleral contact lenses to the target patient population in terms of safety. This retrospective study was conducted across a wide spectrum of ophthalmic contact lens fitting centres and clinics across Australia, New Zealand, and Singapore. This study provides confirmation that the fitting of scleral contact lenses, specifically those with bi-tangential peripheral design, creates beneficial visual outcomes for patients. It is notable that no adverse outcomes were reported for any of the eyes at the review consultations. Patients experienced significant improvements in visual acuity with scleral lenses compared to spectacle correction or their uncorrected visual state. Most patients represented in this study wore lenses for management of corneal irregularity, providing an indication for the use of scleral contact lenses to manage visual outcomes for patients in this category. Dry eye patients also showed evidence of benefit from scleral contact lens wear in management of their dry eye. The bi-tangential scleral contact lens design from Capricornia Contact Lens represents an effective clinical tool that may be employed across the wide population of patients with ocular surface pathology with confidence. This education article is sponsored by Capricornia Contact Lens. To earn your CPD hours visit mieducation.com/ bi-tangential-scleral-cls-drawing-a-straight-line-toclinical-success. References 1. Ye P, Sun A, Weissman BA. Role of mini-scleral gaspermeable lenses in the treatment of corneal disorders. Eye Contact Lens, 2007,33(2):111-11 2. Yildiz E, Toklu MT, Vural ET, Yenerel NM, Bardak H, Kumral ET, et al. Change in Accommodation and Ocular Aberrations in Keratoconus Patients Fitted with Scleral Lenses. Eye Contact Lens, 2018,44 Suppl 1:S50-S53 3. Alipour F, Kheirkhah A, Jabarvand Behrouz M. Use of mini scleral contact lenses in moderate to severe dry eye. Cont Lens Anterior Eye, 2012,35(6):272-276 4. Alipour F, Behrouz MJ, Samet B. Mini-scleral lenses in the visual rehabilitation of patients after penetrating keratoplasty and deep lamellar anterior keratoplasty. Cont Lens Anterior Eye, 2015,38(1):54-58David Stephensen BAppSc (Hons) (Optom), BBus, GradCertOcTher, CO, FCCLSA, FBLCA is the principal of David Stephensen Optometrist in Moorooka, Brisbane. He is a Fellow of the Cornea and Contact Lens Society of Australia and a past National President and Honorary Vice President. Mr Stephensen is also a Fellow of the British Contact Lens Association and an Associate Member of the International Society of Contact Lens Specialists. 5. Yan P, Kapasi M, Conlon R, Teichman JC, Yeung S, Yang Y, et al. Patient comfort and visual outcomes of miniscleral contact lenses. Can J Ophthalmol, 2017,52(1): 69-73 6. Worp E, Graf T, Caroline PJ. Exploring beyond the corneal borders. 2010 7. Eef V. A Guide to Scleral Lens Fitting (2 ed.). 2015 8. Hall LA, Hunt C, Young G, Wolffsohn J. Factors affecting corneoscleral topography. Invest Ophthalmol Vis Sci, 2013,54(5):3691-3701 9. Australian Standard Classification of Cultural and Ethnic Groups (ASCCEG) (2019), Accessed 19/8/2022: Australian Standard Classification of Cultural and Ethnic Groups (ASCCEG), 2019 | Australian Bureau of Statistics (abs.gov.au) 10. Schornack MM, Patel SV. Scleral lenses in the management of keratoconus. Eye Contact Lens, 2010,36(1):39-44 11. Kreps EO, Pesudovs K, Claerhout I, Koppen C. Mini-Scleral Lenses Improve Vision-Related Quality of Life in Keratoconus. Cornea, 2021,40(7):859-864 12. Akkaya Turhan S, Ozarslan Ozcan D, Toker E. Use of a Mini-Scleral Lens in Patients with Keratoconus. Turk J Ophthalmol, 2020,50(6):339-342 13. Shorter E, Harthan J, Nau CB, Nau A, Barr JT, Hodge DO, et al. Scleral Lenses in the Management of Corneal Irregularity and Ocular Surface Disease. Eye Contact Lens, 2018,44(6):372-378 14. Suarez C, Madariaga V, Lepage B, Malecaze M, Fournie P, Soler V, et al. First Experience with the ICD 16.5 Mini-Scleral Lens for Optic and Therapeutic Purposes. Eye Contact Lens, 2018,44(1):44-49 15. Jones L et al, TFOS DEWS II Management and Therapy Report, The Ocular Surface, 2017, 15(3): 575-628
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